Historically, fibrous structures, such as fibrous structures that are used to make sanitary tissue products, have been made with softwood fibers and hardwood fibers. For example, softwood fibers have typically made up greater than 20% by weight on a dry fiber basis of through-air-dried fibrous structures. The softwood fibers are longer fibers than the hardwood fibers and they provide greater strength properties to the fibrous structures than do the hardwood fibers. However, softwood fibers negatively impact the softness of the fibrous structures.
Formulators have for years attempted to balance the level of softwood fibers in their fibrous structures to ensure adequate strength of the fibrous structures while at the same time trying to minimize the level of softwood fibers to avoid negatively impacting the softness of the fibrous structures. The problem has been that formulators have been unable to reliably make fibrous structures, especially through-air-dried (“TAD”) fibrous structures that are used to make sanitary tissue products that contain less than 20% by weight of softwood fibers on a dry fiber basis of the fibrous structure, due to lower resulting strength in the fibrous structures which can lead to product quality issues and/or sheet breaks during processing. If formulators use less than 20% by weight on a dry fiber basis of softwood fibers to make fibrous structures and/or sanitary tissue products, the softwood fibers would need to have excessive refining and/or chemical strength agents to achieve the desired level of strength needed for product quality and/or reliability (avoid sheet breaks during making and/or processing). Both of these actions negatively impact softness of the fibrous structure and/or sanitary tissue product.
Accordingly, there is a need for a fibrous structure that comprises less softwood fibers, for example a 5% or more by weight reduction on a dry fiber basis, than traditional fibrous structures, especially traditional through-air-dried fibrous structures, without negatively impacting the strength of the resulting fibrous structures and reducing machine reliability, sanitary tissue products comprising same and methods for making same.